Digital clock mechanism

ABSTRACT

A digital read-out display type of electric clock or alarm clock uses back projection of light as a means of displaying numerals representing the time in hours, minutes, and seconds upon a front screen. Means are provided to shut off the light projection when the numerals are altered, and the alteration of numerals is carried out in a fraction of a second.

United States Patent Kovacevic 1 July 4, 1972 154] DIGITAL CLOCKMECHANISM 2,486,425 11/1949 Loewe et a1. ..353/40 [72] Inventor:Radoslav Kovacevic, 300 North State l 5 3406, 60610 3:136,2l0 6/1964Barrett ..ss/so R [22] Filed: March 26, 1971 v 1 3,179,003 4/1965Tompson ..58/50 R 2,875,668 3/1959 McKenzie .....58/50 R 1 1 pp 128,3083,439,492 4/1969 Gravenson .5850 R Primary Examiner-Richard B. Wilkinson[52] US. Cl. ..58/50 R, 58llgg3ljag4gls773i Assistant Examiner stanleyA. wal 51 Int. Cl. ..G04b19/30,G03b 21 00, G040 17/02 Rathbum [58] FieldolSearch ..58/50 R, 125 R, 125 B, 2; [57] ABSTRACT A digital read-outdisplay type of electric clock or alarm clock 5 References Cited usesback projection of light as a means of displaying numerals representingthe time in hours, minutes, and seconds upon a UNITED STATES PATENTSfront screen. Means are provided to shut off the light projection whenthe numerals are altered, and the alteration of nul ,21 8,607 3/l9 l 7 W1l1ens "58/50 R metals is carried out i a fraction f second. 1,137,5124/1915 M111er.... 2,35 1,238 6/1944 16 Claims, 11 Drawing Figures Teuber..5 8/50 R DIGITAL CLOCK MECHANISM BACKGROUND OF THE INVENTION Thepresent invention relates to clock mechanisms, and more particularly todigital clock mechanisms wherein the time is indicated by a series ofnumerals or digits which are altered periodically so that the numeralsalways display the time of day.

Digital clocks presently available can be broadly divided into twogroups: Large digital clocks, used in public places or buildings andoutdoors, and small digital clocks, such as table models used in homesand offices.

Large digital clocks come in two types. One type uses electric bulbs toform the numerals and a switching mechanism to control the lighting ofthe bulbs and to provide the proper configuration of lighted bulbs toform numerals. The other type uses flip-cards of a type which aredescribed in more detail below. The first type, using bulbs, isgenerally found outdoors, the second type, using flip-cards, is foundmostly in building lobbies and in public places.

Small clocks, such as table model clocks, use several methods fornumeral display. One type uses rotating drums the edges of which carryimprinted numerals. A first drum (which is sometimes omitted) rotatescontinuously and indicates the time in seconds. Two drums are used toindicate the time in minutes, one for the units digit and one for thetens digit. The last drum indicates the time in hours and has 12numerals. These three last mentioned drums do not turn continuously asdoes the first drum, but turn one numeral position at a time. The timeinterval required for this clock to change its numerals is slow and iscomparatively long lasting. One full rotation of the first drum isrequired to cause the second drum to turn one tenth of a revolution,thus changing the reading on the second drum to the next digit. One fullrevolution of the second drum is similarly required to advance the thirddrum to the next digit. One full revolution of the third drum is alsorequired to advance the fourth or hour drum to the next numeral.

A second type of both large and small size digital clocks uses onesteadily rotating drum (that is sometimes omitted) to indicate the timein seconds and two additional drums, one to indicate the time in minutesand the other to indicate the time in hours. The two additional drumscarry a corresponding number of flip-cards attached around theirperipheries. The minute drum rotates once each hour, and the hour drurnrotates once each 12 or 24 hours. A special mechanism releases eachindividual card, and the cards flip, or fall down over the previouscards covering the old numeral and exposing a new numeral. Normally thefront and back of each card is used to increase the effective size ofthe numerals, and hence two cards are simultaneously used to representeach numeral. The numerals flip quickly in comparison to the slowmovement of the drums in the first mentioned type of small digitalclock.

A third type of small digital clock is electronic and contains no movingparts. This third type of digital clock uses digital read-out electronictubes for numeral display.

All of the above described types of digital clocks have their inherentlimitations and disadvantages. The large digital clocks using lightedbulbs necessarily contain complex electric circuits and elaborateswitching mechanisms. These large clocks contain many lamps or bulbswhich have to be changed periodically. Mechanisms in this type of clockcannot be adapted to display the time in seconds because no electricalcontactor could last long enough to provide the constant switchingrequired to display the time in seconds. The small size'of digital clockin which the numerals are carried by rotating drums shifts the numeralsso slowly that two partial numerals are displayed for substantiallengths of time. This mechanism is far too slow to ever be suited fordisplaying the time in seconds digitally. Digital clocks which useflip-cards are relatively noisy and can disturb the sleep of someindividuals. Also, a visible searnline exists across the middle of thenumerals where the two flip-cards meet. Both flip-card" and drum-typedigital clocks are difficult to design in that some of the workingmechanisms, such as gears, levers, etc., are necessarily visible.Additionally, neither is visible in the dark. A display window or framefor flip-cards or drums must be provided, and this display windowimposes a serious limitation on the freedom with which the clock housingand face may be designed. The electronic digital clock is comparativelyexpensive and cannot be manufactured at low cost, and the electronicnumeral displays do not leave the clock designer much room to choose theshape of his numerals.

A disadvantage inherent in all prior mechanical digital clock designs isthe omission of a set of digits to display the time in seconds. Thisomission is serious because it cannot be easily overcome. A useful clocklife of 10 years encompasses over 310,000,000 seconds. No existingdigital clock design, with the exception of the electronic design, iscapable of providing such a high number of repeated operations. This isthe main reason that the digital display of seconds is omitted from allmechanical digital clocks.

' SUMMARY OF THE INVENTION A primary object of the present invention isto overcome various defects and shortcomings in the clock mechanismsdiscussed above. Other objects are to provide a digital clock which candisplay numbers by projecting them upon a screen, which can mask themovement of numerals during the time intervals when the numerals arechanged, which is virtually noiseless, and which is adaptable to bothindoor use and outdoor advertising use.

In accordance with these and other objects, an embodiment of the presentinvention comprises briefly a digital clock wherein the numerals arelocated on the transparent surfaces of three planar gear assemblies. The60 numerals from 0 to 60 or five sets of the numerals from 0 to 12 arelocated on each gear assembly. A constantly rotating driver-pacer gearsupplies motive power. The three gear assemblies and the driverpacergear are interconnected by pinion gears in such a manner that each gearassembly rotates one-sixtieth of a revolution when the preceding gearadvances from the last numeral on its face to the first, or in the caseof the first gear assembly when the driver-pacer gear rotates a fixedamount. A light diffusing screen is provided at the front of the clock,and an optical mechanism associated with each gear assembly projects asingle numeral from the gear assembly onto the screen to display thetime digitally in hours, in minutes, and in seconds. By avoiding the useof such items as moving springs and levers and by using only gear powertrains, wear in the clock mechanism is reduced to an absolute minumum.The loading on the gear power train is dept small because the mechanismdoes nothing but drive itself and deflect light beams. The speed of gearmotion and the gearing tooth arrangement are also optimized to minimizewear, as is explained below. The pinion gears drive masks which blankout the numerals during the brief time intervals when the numerals arechanged and which thus give the appearance of almost no motion when thenumerals are changed. The time setting of the clock is adjusted byrotating one half of a gear assembly or pinion gear independently of theother half of the assembly or gear. A ratchet mechanism insures that thetwo halves mesh properly after the time setting has been made.

Another embodiment of the present invention is similar in design to theabove embodiment in its use of gear assemblies but places numeralbearing rotating members adjacent the front of the clock so that thenumerals are projected without the aid of lenses. Since the numerals inthis embodiment are larger, this embodiment requires five gearassemblies and pinion gears, rather than three, to give a completedigital display in time.

Further objects and advantages of the present invention are apparent inthe detailed description which follows. The points of novelty whichcharacterize the invention are pointed out with particularity in theclaims annexed to and forming a part of this specification.

BRIEF DESCRIPTION or THE DRAWINGS FIG. 1 is a sectional, plan view takenalong the line 1-1 in FIG. 2 of a digital clock having an alarmprovision incorporated into the clock mechanism.

FIG. 2 is a longitudinal, sectional view taken along the line 22 in FIG.I of the inside of the digital clock with some of the parts removed forclarity.

FIG. 3 is a partially sectional, plan view of an alternative clockmechanism for use in the clock shown in FIG. 1.

FIG. 4 is a cross-sectional view taken along the line 44 in FIG. 1 ofthe digital clock.

FIG. 5 is an isometric view of certain major gear parts of the clockmechanism enlarged for clarity.

FIG. 6 is a front, elevational view of the face of the clock shown inFIG. 1.

FIG. 7 is a sectional, plan view of a second version of the digitalclock with the alarm provision omitted for clarity.

FIG. 8 is a longitudinal, sectional view taken along the line 8-8 inFIG. 7 of the digital clock shown in FIG. 7.

FIG. 9 is a longitudinal, sectional view taken along the line 9-9 inFIG. 7 of the digital clock shown in FIG. 7.

FIG. 10 is a cross-sectional view taken along the line 10-10 in FIG. 7of the digital clock shown in FIG. 7.

FIG. 11 is a front, elevational view of the face of the clock shown inFIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a digitalread-out clock with optional alarm includes an electrical and mechanicalsystem for keeping the right time and for changing the numerals whichare displayed. This clock utilizes an optical lens system for backprojection of light as a means of digital display. The clock is shown inFIGS. 1 to 6 and is indicated by the reference numeral 1 1. The mainelements of this clock are: a clock enclosure with a back projectionscreen; electrical and mechanical means for keeping time and forchanging the numerals; electrical and optical means for back projectionof the numerals onto the screen; and an optional provision for alarm.The clock enclosure consists mainly of a rectangular box with a fromscreen of ground glass or diffuse plastic for digital back projectionand a back closure plate for access and bulb change.

The electrical and mechanical means for keeping time and for changingthe numerals include a synchronous electric motor 24 which rotates at aconstant speed. The motor rotation is transmitted directly to adriver-pacer gear 28 which transfers the rotation to a series of piniongears and gear assemblies in such a manner as to supply to each gearassembly serving the digital display of seconds, minutes, and hours theproper speed and type of movement to satisfy each digital read-outdisplay. A gear assembly 50 which digitally displays the time in secondsrotates through one-sixtieth of a revolution each second. Once everyminute the gear assembly 50 completes a full revolution and advances thenext gear assembly 54 by one-sixtieth of a revolution. The assembly 54digitally displays the time in minutes. One full revolution of the gearassembly 54 takes I hour to complete. Once each hour the gear assembly54 completes a full revolution and advances the next gear assembly 58 byone-sixtieth of a revolution. The assembly 58 digitally displays thetime in hours. The gear assembly 58 has 60 increments just as do thegear assemblies 50 and 54, even though the hours display has only 12numerals. This simplifies the clock design and allows use of the samemanufactured parts for constructing all three of the gear assemblies 50,54, and 58. The hours gear assembly 58 contains five 12 hour digitaldisplays, or 60 displays total. The type of movement which results inall three of the digital displays--for seconds, for minutes, and forhours-consists of a quick, incremental movement of one-sixtieth of onefull revolution. This movement lasts only a fraction of a second. Meansare provided to keep the gears stationary between such movements, andadditional means are provided to blank the display during suchmovements.

The electrical and optical lens system includes an electric transformer122 which supplies low voltage electrical current to three low voltagebulbs 124. The bulbs 124 serve as light source, one for each digitaldisplay. The light rays are condensed by three condensing lenses 128,passed through the numeral bearing member gear assemblies 50, 54, and58, and projected by three projecting lenses 130 through threestationary masks 140 onto a screen 2 at the front of the clock 11. Othermoving masks interrupt the light rays and the projection during thetimes when the display numerals change. Numerals are imprinted upon thethree main gear assemblies 50, 54, and 58. These gear assemblies aremade of transparent plastic and serve as carriers of the numerals.

The optional alarm provision consists basically of two adjacent discs.One of the two discs 152 is connected to the clock mechanism andrevolves once in 12 hours. The other disc 156 bears engraved numerals158 with 12 hour divisions and may be set manually to any desired alarmtime. As the first disc 152 rotates, the first disc 152 reaches a pointwhere it makes contact with the second, manually set disc 156. Means areprovided to sound an alarm when this contact is established.

The above description is a brief explanation in general terms foroverall orientation. The following is a detailed description of allparts and of the functioning of the digital read-out clock.

In FIGS. 1, 2, 4, and 6, a from screen 2 for back projection is held inplace by a screen frame 4 which is fastened to the body of the clock 11enclosure 6 which has legs 8 and which has a back closure plate 10fastened to the clock enclosure 6 by fasteners 12. The back closureplate 10 has an oversized hole 14 which allows protrusion of a timesetting knob 16 from the back of the clock 11.

The clock mechanism includes two carrying plates, a front carrying plate18 and a back carrying plate 20. The plates 18 and 20 are held apart andare secured by spacers 22. A constant speed synchronous motor 24 isfastened to the front carrier plate 18. An aide 26 of the motor 24carries a driver-pacer gear 28 and rotates the gear 28 one completerevolution every four seconds. The rotation of the gear 28 istransferred to a first pinion gear 36 which in turn controls therotation of a first main gear assembly 50. The gear assembly 50 presentsthe seconds digital read-out. The gear assembly 50 is meshed with asecond pinion gear 52 which transfers the movement of the assembly 50 tothe gear assembly 54. The assembly 54 presents the minutes digitalread-out. The gear assembly 54 is in turn meshed to a third pinion gear56 which transfers motion to a third main gear assembly 58. The assembly58 presents the hours digital read-out.

The transfer of motion from the driver-pacer gear 28 or from any gearassembly 50, 54, or 58 to a pinion gear 36, 52, or 56 is accomplished inthe following manner. By way of illustration, the description refers tothe transfer of motion between the gear 28 and the pinion gear 36. Thedriver-pacer gear 28 has a circular periphery 60 which is interrupted atfour locations by grooves 62 equally spaced around the periphery 60 andby four two-tooth gear segments 64 spaced on either side of and adjacentto each groove 62. The synchronous motor 24 rotates at a speed of 15 RPMand completely revolves the driver-pacer gear 28 once every 4 seconds.Since the gear 28 has four two-tooth gear segments 64, the gear 28engages and turns the pinion gear 36 which is mounted on an axle 66 onceevery second. The pinion gear 36 includes two pinion halves, a firsthalf 68 having eight teeth (see FIG. 5), and a second half 70 which hasevery second tooth omitted and which is an incomplete, cross-shaped gearhaving only four teeth. The shape and form of this first pinion gear 36serves a two-fold function: First, it keeps the gear assembly 50 in afixed position during the time when a numeral is projected onto thescreen 2; and secondly, it quickly turns the main gear assembly 50 theamount of one numeral (or one-sixtieth of one revolution) each time thedriver-pacer gear 28 completes one-fourth of a revolution. The main gearassembly 50 is held in a fixed position because the periphery 60 of thegear 28 slides against two teeth of the cross-shaped gear half 70 of thepinion gear 36. The teeth of the gear half 70 are positioned snuglyagainst the periphery 60 of the gear 28 and cannot turn, as is shown inFIG. 5. The teeth 70 thus hold the next main gear assembly 50 and allthe other pinion gears and gear assemblies immobile. When one of thegear segments 64 engages the pinion 36, it engages the eight-tooth half68 of the pinion 36 and rotates the pinion gear 36 for one-fourth of arevolution or two teeth positions. The cross-shaped half 70 of thepinion gear 36 is allowed to turn at the same time because the periphery60 is interrupted by one of the grooves 62. This turning occurs everytime one of the four two-tooth gear segments 64 of the gear 28 engagesthe pinion gear 36.

The movement of a pinion gear 36, 52, or 56 is transferred to a gearassembly 50, 54, or 58in the following manner. The pinion gear 36 andthe gear assembly 50 are described as exemplary of the others. The gearassembly 50 is constructed out of two halves. A first half 72 is amovement receiving gear having 120teeth. A second half 74 is a movementtransmitting gear, with one groove 76 and a two-tooth gear segment 78similar to the four grooves 62 and two-tooth gear segments 64 on thedriver-pacer gear 28. The groove 76 in the half 74 is located betweenthe two teeth of the two-tooth gear segment 78. The two halves 72 and 74are held together by an axle 80 and move as a single unit. As the piniongear 36 rotates onefourth of a revolution, the eight-tooth half 68 turnsa distance equal to two teeth positions. The eight-tooth half 68 ismeshed to the movement receiving half 72 of the main gear assembly 60.The gear 72 contains 120 teeth and thus rotates one-sixtieth of arevolution or the amount of one numeral. After the movement isaccomplished, the first main gear assembly 50 is held motionless duringthe digital display by the pinion gear 36 until the next change innumerals occurs one second later.

The transfer of motion down the remaining portions of the power train iscarried out in the same manner as the illustrative transfers describedabove and thus needs no detailed explanation. The gear assembly 50completes one complete revolution each minute and causes the pinion gear52 to advance the gear assembly 54 by one-sixtieth of a revolution atthe end of every minute. The gear assembly 54 completes one revolutioneach hour and causes the pinion gear 56 to advance the gear assembly 58by one-sixtieth of a revolution at the end of every hour. All assemblyrotations are carried out in a fraction of a second. The gear assemblies50, 54, and 58 all rotate at the same high speed when they are advanced.The digits are thus never in motion for more than a brief part of asecond. The third main gear assembly 58 does not have any motiontransmitting component since it is the last in the line of pinions andgears and no transfer of movement from it is necessary. It is simpliest,however, to include a motion transmitting component on the third gearassembly 58 so as to keep the three main gear assemblies identical toone another.

Other components, not identified so far, are: The movement receivinghalf 86 and the movement transferring half 88 of the second main gearassembly 54, and its axle 90; the axles 84 and 92 of the second andthird pinion gears 52 and 56, their eight-tooth gear halves 80 and 94and four-tooth gear halves 82 and 96; and the movement receiving half100 and the optional movement transferring half 102 of the third maingear assembly 58, and its axle 104.

A special mechanism is provided for allowing the initial setting of thetime indication. This mechanism provides for adjustment of the timesetting for minutes and hours only, since the exact setting of the timein seconds is best accomplished by starting the clock at the exact timein seconds displayed upon its face. Minute setting is carried out byturning the movement transferring half 88 of the second main gearassembly 54 to set the gear assembly 54 to the desired minute reading.If there is need for hour setting also, the movement transferring half88 is turned as many full revolutions as are required to give thedesired hour setting. The time setting operation is accomplished bymanual rotation of the move ment transmitting half 88. The half 88carries printed minute numerals 106 (FIG. 2), and thus its movement canbe monitored on the front screen 2 of the clock 1 1. The turning of onlythe one half 88 of the main gear assembly 54 for minutes is madepossible by provision for independent movement of the two halves 86 and88 of the assembly 54. The turning of the movement receiving half 86 isdependent only upon the tuming of the second pinion gear 52, and thehalf 86 is normally locked in a fixed position. When movement of thepinion 52 occurs, the movement is normally transferred to the movementtransferring half 88 of the main gear assembly 54; however, during thetime setting operation, the normal clock operation is overridden by themanual manipulation.

The following is a description of the parts that make up the provisionfor manual time setting. A setting knob 16 actuates an axle whichprotrudes through the oversized hole 14 in the back plate 10. A disc 108fastened to the axle 90 prevents the light from leaking out of the clock11 enclosure. The movement transferring half 88 of the main gearassembly 54 is affixed to a thicker portion 110 of the axle 90 and thusturns with the axle 90. The movement receiving half 86 of the main gearassembly 54 is located at a thinner portion 112 of the axle 90 and isnot afiixed to the axle 90. The axle 90 and the half 86 thus may rotateindependently. During normal operation of the clock 11, movement istransferred from the movement receiving half 86 to the movementtransferring half 88 by 60 shallow, V-shaped grooves or notches 114(FIG. 2) moulded into the plastic body of the half 88 to form a ringaround the axle 90. Each of the notches 114 corresponds to the positionof one of the 60 numerals 106 on the gear assembly 54. Three of thenotches 114 normally engage three equally spaced, V- shaped projections116 (HO. 1) cast into the plastic body of the half 86 and located at thesame distance from and around the axle 90 as the notches 114 on the half88. The projections 116 and the notches 114 keep the turning positionsof the two halves 86 and 88 related to eachother in one of the possible60 fixed positions each of which corresponds to one of the 60 numeralscarried by the gear assembly 54. During normal clock operation, a coilcompression spring 118 on the axle 90 pushes against a gear 120 that isfastened to the axle 90 and pushes the movement receiving half 86 of thegear assembly 54 against the movement transferring half 88. As aconsequence, the three projections 116 of the one half 86 are pushedinto he V-shaped notches 114 of the other half 88, keeping both halveslocked together and causing both halves to turn as a single unit. Duringthe time setting operation, however, the movement receiving half 86 ismeshed with the second pinion gear 52 and cannot turn until the piniongear 52 turns. In order to set the time, the movement transferring half88 carrying the imprinted numerals 106 must rotate, and the bond keepingthe two halves 86 and 88 locked together must be broken. This isaccomplished by manual rotation of the setting knob 16 which is securelyfastened to the movement transferring half 88, and by applying enoughforce to the knob 16 to override the bond between the V-shapedprojections 116 and V-shaped notches 114 caused by the pressure of thecompression spring 118. The projections 116 then jump out of the notches114 and allow the movement transferring half 88 to be turned to thedesired minutes setting. The three projections 116 then click-set intothree other notches 114 corresponding to the new time setting. The 60click-settings provided by the projections 116 and notches 1 14 arenecessary to limit the relative locked positions of the two halves 86and 88 to the 60 fixed positions each of which corresponds to one of the60 numerals carried by the half 88 and to prevent the clock 11 fromreaching a setting intermediate between two numerals. The time settingmay be monitored on the front screen 2. The movable mask 134 whichnormally blocks the projection of the numerals during normal clockoperation stays in open position during time setting operations becauseits movement is dependent only upon movement of the second pinion gear52.

, The initial time setting of the hours time indication is accomplishedby continuous rotation of the setting knob 16. Each full revolution ofthe knob 16 causes the gear assembly 58 which displays the time in hoursto advance to the next hour setting.

The setting knob 16 may be turned in both the clockwise and thecounterclockwise directions. If the clock has provision for sounding analarm, the rotation should be in a clockwise direction if it isimportant that the alarm setting not be disturbed.

The time setting provision just described may be extended to include aseparate time setting provision for seconds and for hours, if desired,by simply adding the same time setting mechanism to the main gearassemblies 50 and 58. This may be easily done since all the main gearassemblies 50, 54, and 58 are constructed from the same components.

The electrical and optical projection system used for the basicprojection of numerals upon the screen 2 includes the following parts. Atransformer 122 supplied three bulbs 124 in three sockets 126 with lowvoltage electric current. The bulbs 124 are of the long life, lowvoltage, low amperage type. Each bulb 124 serves as the light source forone of the three digital display systems and has a condensing lens 128and a projecting lens 130. The lenses 128 and 130 are glued intoposition inside dish-like round openings 132 in the front and backcarrying plates 18 and 20. Numerals 106 (FIG. 2) are imprinted as clearnumerals with a black background on the plastic transparent discs whichform one of the two halves of the three main gear assemblies 50, 54, and58. The numerals 106 are imprinted on the movement transferring half 88of the second main gear assembly 54 and on the movement receiving halves72 and 102 of the main gear assemblies 50 and 58. The reason for this isthat the positioning of the movement receiving and the movementtransferring halves alternates from one main gear assembly to the next(see FIG. but the distance between the numeral objects and lenses iskept uniform in all three cases to that the same uniform rate ofmagnification is achieved in all three of the digital displays.

During the change of numbers, image projection is blocked by masks 134which are circular discs each having four windows 136. The masks 134 aremounted on the axles 66, 84, and 92 to which are attached the piniongears 36, 52, and 56. During digital display, light rays 138 (FIG. 1)travel through the windows 136. During the change of numerals, thepinions 36, 52, and 56 rotate for one-fourth of a revolution and forcethe masks 134 to also rotate one-fourth of a revolution. In doing so,the windows 136 move out of the path of light rays 138 and the soliddisc areas between the windows 136 come into the path of light. Hence,the projection of light is interrupted while the numerals are changed.After the change of numerals is completed, another window 136 moves intothe path of the light rays 138 and allows projection to resume.

The light rays 138, on their way to the screen 2, pass through set ofstationary windows 140 in a stationary mask 142. The mask 142 blocks outthe projection of neighboring numerals and lets only the light image ofthe desired numerals reach the screen 2. The light rays 138 (FIG. 1)which reach the screen 2 form an image or digital display 144 (FIG. 6)which can be observed from the front of the clock 11. The screen 2 ismade of ground glass, of light diffusive plastic, or of some similarmaterial.

The optional alarm comprises a series of gears which reduce the speed ofrotation of the main gear assembly 54 from one revolution per hour toone revolution per 12 hours. The movement starts with a pinion 120 thatrotates at a speed of one revolution per hour and that has 12 teeth. Themotion of the pinion 120 is transferred to a gear 146 having 48 teethand to a pinion 148 having teeth which gear and pinion are both carriedby an axle 150. Another gear 152 is meshed to the pinion 148 and rotatesone revolution every l2 hours. An axle 154 carries both the gear 152 andthe alarm setting disc 156. The disc 156 has a flat area 158 onto whichhour and quarter hour divisions are engraved and has a serrated edge 160to assist one in manually turning the disc 156 to the desired alarmtime. The disc 156 protrudes through to the oumide of the clock 11housing 6 through an opening 162 (FIG. 4). The opening 162 facilitatesthe reading and the setting of the alarm time. Surrounding the opening162 is a plate 166 which bears an engraved arrow (not shown) that pointsto the alarm time engraved on the disc 156. The disc 156 has a provisionfor restraining its free movement by the inclusion of a spring washer168 (FIG. 4) which is placed between the front carrying plate 18 and apin 170 in the axle 154. The spring action restrains the free movementof the axle 154. The gear 152 has a central sleeve 172 which allows itto freely rotate around the axle 154 and to move in a longitudinaldirection. A compression coil spring 174 pushes the gear 152 against thealarm setting disc 156. They are held a small distance apart by atriangular protrusion 176 in the gear 152 which is stamped out' and bentto 90, leaving a triangular hole 178 in the gear 152. As the gear 152slowly rotates, the triangular protrusion 176 ultimately reaches thelocation of a slit 180 in the alarm setting disc 156, and the protrusion176 enters the slit 180 due to the pressure of the spring 174 upon thegear 152. This longitudinal motion parallel to the axis of the axle 154actuates an alarm mechanism (not shown). The details of the alarmmechanism are beyond the scope of the present invention and are notshown in the drawings. Any suitable alarm mechanism may be used.

An alternate way to initially set the time and to reduce the number ofmolded plastic parts is shown in FIG. 3. The main gear assemblies 200,202, and 204 for seconds, minutes, and hours are the same productionparts made of one piece. They each contain movement receiving half 206,which is a gear with 120 teeth, and a movement transferring half 208,which is a disc with one groove and one two-tooth gear segment. Timesetting is accomplished by providing second pinion gear 210 that is madeout of two halves 216 and 218 which turn independently of one anotherduring the time setting operation and which turn in unison during normalclock operation. A setting knob 212 is attached to an axle 214 whichcarries the eight-tooth half 116 of the pinion gear 210. The fourtooth,cross-shaped half 218 of the pinion gear 210 is carried on a sleeve 220and turns independently around the axle 214. The sleeve 220 carries onits other end a two-pronged spring 222. The prongs 224 of the spring 222fit into indentations 226 in a disc 228 which is attached to the axle214. The disc 228 carries four equally spaced indentations 226. The twoprongs 224 fit into two of the indentations 226, and this action of thespring 222 forces the two components of the pinion gear 210 to normallyturn in unison. During the time setting operation, the action of thespring 222 is overcome by manual rotation of the time setting knob 212,the axle 214, and eight-tooth pinion half 216, and the disc 228. Thecross-shaped, incomplete, four-tooth segment 218 of the pinion 210 doesnot turn because it is wedged against the movement transferring half 208of the first gear assembly 200. Consequently, the sleeve 220 and thespring 222 do not turn either. When the disc 228 is forced to turn, theprongs 224 of the spring 222 jump out of their position in the discindentations 226, and they fall in and out of the indentations 226 foras long as the disc 228 continues to rotate. The turning action of theeight-gear component 216 of the pinion 210 turns the gear assembly 202until the required setting of time is reached. The prongs 224 of thespring 222 then settle into one of the four possible positions in theindentations 226 on the disc 228, the two-pinion halves again lock intoone of the four possible positions relative to each other, and normalclock operation commences once more. The continuous rotation of the maingear assembly 202 for minutes causes the main gear assembly 204 forhours to rotate, as was shown in the previous example. Thus, the time inhours can also be set by rotation of the knob 212. If desired, the timesetting arrangements may be extended, and the main gear assemblies 200and 204 for seconds and for hours may be equipped with their ownindependent time setting mechanisms.

Provision for alarm operation may be added to the clock shown in FIG. 3and may be constructed in the same manner as that shown in FIG. 2. Thestarting point for the alarm drive is a gear 230 having 12 teethcorresponding to gear 120 shown in FIG. 2.

In designing a digital clock mechanism, special attention must be paidto the features which decrease wear on all moving parts. The clockdesign is based on the premise that the only moving parts other than themotor which are used to keep time and to change numerals are gears andgear trains. Thus, the main concern is the surface deterioration of gearteeth, notably the teeth of the driver-pacer gear 28 and the teeth ofthe first pinion gear 36. These teeth make the greatest number ofcontacts because they control the digital display of the time inseconds. Numerous factors affect the surface wear of gear teeth. Listedhere are some more obvious ones: The wear on the teeth is directlyproportional to the total number of contacts the teeth make, to theamount of load which the teeth have to transfer, to the kinetic energywhich is created by the impact between the teeth and which has to beabsorbed by the teeth in overcoming inertial energy, to the size of thecontact area of the teeth, and to the coefficient of wear of the teethmaterial. Thus, the goals in the design of digital clock gears are: Tohave the greatest number of teeth possible in a driver-pacer gear and inthe first pinion; to reduce the load which the teeth have to carry; tominimize impact energy; to increase the contact area between the meshingteeth; and to make the teeth of a long wearing material. The number ofteeth in the driver-pacer gear was chosen to be four two-tooth gearsegments or a total of eight teeth. The reason for not having more thaneight teeth is that the first pinion with which they mesh has only eightteeth, and the longevity of the pinion gear is thus the limiting factor.The total number of contacts which the driver-pacer gear has to make isreduced by four, since there are four two-tooth segments which divideamong themselves the total work load. The load which the teeth have totransfer can be kept to a minimum, since the only force which must beovercome is the force necessary to turn the gears and pinionsthemselves, and this is dependent upon the friction of the bearings andalso upon the gear meshing. These factors can be controlled by properbearing choice and by proper gear design. The reduction of impact energyis dependent upon keeping the rotational inertia of the parts to aminimum by constructing the gears from plastic, including the rotatingmasks. The speed of motion of the two-tooth segments 64 of thedriver-pacer gear 28 depends upon the selected number of two-toothsegments, the resulting number of revolutions per minute, and the sizeof the driver-pacer gear itself. Four two-tooth segments of thedriver-pacer gear 28 require a drive speed of 15 RPM for the gear 28.This combination produces one contact of the two-tooth segments 64 withthe first pinion gear 36 every second. The diameter of the driver-pacergear 28 detcnnines the speed with which the segments 64 move around theperiphery of the gear 28. The driver-pacer gear 28 is given a diameterequivalent to that of a gear having 40 teeth of the same size as theteeth which comprise the segments 64. Since the driver-pacer gear 28rotates once every 4 seconds, the time required for each tooth on thegear 28 to pass a fixed point is one-tenth of a second. Since there aretwo teeth in each of the two-tooth segments, it then takes one-fifth ofeach second for each segment 64 to rotate the first pinion one-fourth ofa revolution and to change the numerals, and the remaining four-fifthsof each second are left for numeral display. This ratio has been foundin actual tests to be satisfactory-the change of the numerals is quickenough, yet the speed of tooth motion is not high enough to produce highimpact forces. Increasing the contact area between the meshing teethmeans increasing the width of the face of the first pinion and the widthof the face of the driverpacer gear. In this design, the face of theteeth of the two above-mentioned gears is wider than the rest of thegear teeth. Finally, a low friction material having good wearingproperties is used for the gear teeth.

An alternate form of digital read-out clock 299 which does not use anoptical lens system for back projection of digits on a screen is shownin FIGS. 7 to 11. The clock 299 uses numeral cut-outs 376 to createnumber images in light. The cut-outs 376 are placed in close proximityto a fogged glass screen and the light reaching the screen is forced topass through the cutouts, thus'delineating images of the numerals on thescreen. The numeral cut-outs 376 are formed on circular metal discswhich rotate to change the numerals. Rotating masks block the lightduring numeral changes, as in the clock 11. Two discs rather than asingle disc are used to display the digits which represent the time inseconds and the time in minutes, and a single disc is used to displaythe time in hours. The discs used to display the units digit of the timein seconds and in minutes each carry the 10 numeral cut-outs from 0 to9, and the discs used to display the tens digit of the time in secondsand in minutes each carry the six numeral cut-outs from 0 to 5. Thesingle disc used to display the time in hours carries the 12 numbersfrom 1 to 12. The discs and masks are operated by a time-keepingmechanism which uses pinions and gear assemblies which are identical tothose used in the clock 11 except that five sets of gear assemblies andpinions are used instead of three. Since there are fewer numerals pergear than in the clock 11, the numerals may be larger in size, and aprojection lens system is not required to magnify the size of thenumerals.

The clock 299 housing includes a rectangular clock enclosure 300 whichis mounted on two legs 302. A screen frame 304 attaches a fogged glassscreen 306 to the front of the enclosure 300. A back closure plate 308gives access to the gears, and a bottom access door (not shown) givesaccess to a lamp 392. The mechanism which keeps the right time andchanges the numerals includes three carrying plates-a front plate 312, amiddle plate 314, and a back plate 316-and four spacers and fasteners318 to hold the three plates together. The back plate 316 carries asynchronous electric motor 320 which through its axle 322 turns adriver-pacer gear 324. The driver-pacer gear 324 transmits movement topinion gears and gear assemblies precisely as previously described forthe clock 11. The pinion gears and gear assemblies in the clock 299 areconstructed in the same manner as the pinion gears and gear assembliesin the clock 11 except that the gear assemblies in the clock 299 neednot be transparent and do not have teeth. The number of teeth on eachgear assembly is chosen to suit the requirements of the digits which thegear assembly displays. The gear assemblies 330 and 346 which displaythe first (or units) digit of the time in seconds and in minutes have 20teeth each. The gear assemblies 338 and 354 which display the second (ortens) digit of the time in seconds and in minutes have 12 teeth each.The gear assembly 362 which displays the time in hours has 24 teeth.

The axles 332, 340, 348, 356, and 364 carrying the gear assemblies 330,338, 346, 354, and 362 also carry discs which support the numeralcut-outs. The axle 332 carries a disc 366 with 10 numeral cutouts 376that serve to display the units digit of the time in seconds; the axle340 carries a disc 368 with six numeral cut-outs 376 that serve todisplay the tens digit of the time in seconds, the axle 348 carries adisc 370 with 10 numeral cut-outs 376 that serve to display the unitsdigit of time in minutes; the axle 356 carries a disc 372 with sixnumeral cut-outs 376 that serve to display the tens digit of the time inminutes; and the axle 364 carries a disc 374 with 12 numeral cut-outs376 that serve to display both digits of the time in hours.

As the main gear assemblies rotate, so do the discs carrying the numeralcut-outs 376. As the discs turn, different numerals appear in windows378 located in a front plate 312. The windows 378 block light frompassing through other numeral cut-outs 376 and reaching the front screen306 (FIGS. 7 and 11). Only the images 380 (FIG. 11) of the numeralcutpear on the front screen 306.

The provision for blocking the projection of images 380 on the frontscreen 306 during numeral changes os constructed in the clock 299somewhat differently than it is in the clock 11, but the provision isstill based upon the same principles of operation. In the case of thefirst digit for minutes, a circular mask 382 with four rectangularopenings 384 is mounted upon a sleeve 386 and is placed over the axle348 that carries the gear assembly 346 and the disc 370. The oppositeend of the sleeve 386 is attached to a gear 388 which is meshed toanother gear 390 that is carried by the axle 344 which also carries thethird pinion gear 342. Both of the gears 388 and 390 have the samenumber of teeth. During the numeral change interval, the pinion gear 342rotates one-fourth of a revolution and causes the gear assembly 346 torotate a new numeral into position for display. As the pinion gear 342turns one-fourth revolution, it rotates the gears 390 and 388 onefourthof a revolution and hence rotates the sleeve 386 and the mask 382one-fourth of a revolution. This rotation removes the rectangularopening 384 in the mask 382 from its location directly behind the window378 adjacent the numeral cut-outs 376, and projection of the images 380(FIG. 11) onto the screen 306 is blocked during the major portion of thenumeral change interval. At the end of the numeral change interval, whenthe next numeral cut-out 376 is positioned behind the window 378 in thefront plage 316, the mask 382 completes its one fourth revolution turn.Another one of the four rectangular openings 384 in the mask 382 movesinto position behind the window 378 and the projection of the nextnumeral image 380 commences. This modified method of projection blockageduring the number change interval is more effective for the clock 299than the method used with the clock 11 because of the more favorableratio which results between the size of the rectangular openings and thespace available between the openings in the circular masks 382.

The time setting mechanism used in the clock 299 is similar to the timesetting mechanism used in the clock 11. The time setting knob 394 isattached to an axle 348 which serves the first (or units) digit of thetime in minutes. Continuous rotation of the knob 348 causes the second(or tens) digit of the time in minutes and the digits for the time inhours to shift. The alternative mechanism for the time setting shown inFIG. 3 may be used in the clock 299, if desired. An alarm mechanismsimilar to that shown in FIGS. 2 and 4 may also be added to the clock299.

Although the present invention has been described with reference to onlya few illustrative embodiments thereof, it should be understood thatnumerous other modifications and changes will readily occur to thoseskilled in the art. It is therefore intended by the appended claims tocover all such modifications and changes as fall within the true spiritand scope of the invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. A digital clock mechanism comprising:

a gear support;

a gear train formed by having a plurality of gears mounted parallelyupon said support, with the edge of each gear engaging the edges of theadjacent gears and with the gears extending longitudinally from one endof the gear train to the other end;

a synchronous motor mounted at one end of the gear train;

a driver-pacer gear at one end of the gear train that is driven by thesynchronous motor, said driver-pacer gear having at least one group ofat least one gear tooth spaced about its periphery and adjacent to atleast one notch in its P y;

pinion gears and gear assemblies comprising the plurality of gears, thefirst pinion gear transferring the motion of the driver-pacer gear tothe first gear assembly, and each succeeding pinion gear transferringmotion from one gear assembly to the next; said gear assemblies eachincluding a fully-toothed periphery for engaging the previous piniongear and a periphery containing at least one tooth and at least onenotch for engaging the next succeeding pinion gear; and said piniongears containing a fully toothed periphery for engaging said tooth onthe preceding gear or gear assembly and the fully toothed periphery ofthe following gear assembly, and a partially toothed periphery forengaging said notch in the preceding gear assembly or driver-pacer gearand for otherwise immobilizing the pinion gear;

numeral carriers each of which is rotated by a gear assembly; and

means for viewing one numeral on each numeral carrier.

2. A digital clock mechanism in accordance with claim 1 wherein at leastone of the gear assemblies includes a first half of the gear assemblythat bears the fully-toothed periphery and a second half of the gearassembly that bears said tooth and said notch, wherein the two halvesare coupled together by a ratchet mechanism comprising pins or lugs onone half which engage notches on the other half and spring means fordriving the two halves together, and which further includes a manuallyactuatable time setting mechanism that attaches to one half of the gearassembly but that does not attach to the other half.

3. A digital clock mechanism in accordance with claim 1 wherein thedriver-pacer includes four groups of two teeth centered about fournotches which are equally spaced around theperiphery of saiddriver-pacer gear, wherein the pinion gears each have eight teeth abouttheir fully toothed periphery and four teeth about their partiallytoothed periphery, wherein the diameter of the driver-pacer gear ischosen in relation to the driver-pacer gear tooth size so thatapproximately 40 teeth of the same size could properly be spaced aboutthe periphery of the driver-pacer gear, and wherein the driver-pacergear is driven at a speed of 15 revolutions per second by a synchronousmotor.

4. A digital clock mechanism in accordance with claim 1 to which hasbeen added an alarm mechanism comprising:

a manually positionable disc bearing the numbers l through 12;

a gear driven through one complete revolution every 12 by means couplingto a gear assembly that rotates at least once every hour; and

means responsive to the disc and the gear reaching correspondingpositions for sounding an alarm.

5. A digital clock mechanism in accordance with claim 1 wherein some ofthe gear assemblies are identically shaped and wherein some of thepinion gears are also identically shaped.

6. A digital clock mechanism in accordance with claim 1 wherein themeans for viewing one numeral on each numeral carrier comprise anoptical system including a source of light positioned on one side ofeach numeral carrier, a screen positioned on the other side of eachnumeral carrier, and stationary masking means for preventing images ofmore than one numeral on each numeral carrier from being projected ontothe screen.

7. A digital clock mechanism in accordance with claim 6 wherein theoptical system includes a condensing lens positioned between the sourceof light and each numeral carrier and a projection lens positionedbetween each numeral carrier and the screen.

8. A digital clock mechanism in accordance with claim 6 wherein arotating masking means including at least one opening is provided foreach numeral array and is positioned to block the passage of lightthrough the numeral array except when a opening is in line with thesource of light, the masking means, and the screen; and wherein eachpinion gear is arranged to rotate the rotating masking means associatedwith the next higher gear assembly in the gear train.

9. A digital clock mechanism in accordance with claim 6 wherein thenumeral carriers are in close proximity to the screen, whereby images ofthe numerals are formed by the light rays from the light source passingthrough the numerals and striking the screen without the aid of lenssystem.

10. A digital clock mechanism in accordance with claim 9 wherein twoarrays of numerals are used to represent the time in seconds, whereintwo arrays of numerals are used to represent the time in minutes, andwherein a single array of numerals is used to represent the time inhours; wherein the arrays of numerals representing the units digit oftime in seconds and in minutes each contain 10 numerals from to 9,wherein the arrays of numerals representing the tens digit of the timein seconds and in minutes each contain six numerals from 0 to 5, andwherein the array of numerals representing the time in hours containsthe 12 numerals from 1 to 12.

11. A digital clock mechanism in accordance with claim 1 wherein atleast one of the pinion gears includes a first half of the pinion gearthat bears the fully-toothed periphery and a second half of the piniongear that bears the partially toothed periphery, wherein the two halvesare coupled together by a ratchet mechanism comprising pins or lugs onone half which engage notches on the other half and spring means fordriving the two halves together, and which further includes a manuallyactuatable time setting mechanism that attaches to one half of thepinion gear but that does not attach to the other half.

12. A digital clock mechanism in accordance with claim 1 to which hasbeen added an alarm mechanism comprising:

a manually positionable disc bearing the numbers 1 through 24;

a gear driven through one complete revolution every 24 hours by meanscoupling to a gear assembly that rotates at least once every hour; and

means responsive to the disc and the gear reaching correspondingpositions for sounding an alarm.

13. A digital clock mechanism in accordance with claim 1 wherein thenumeral carriers and the gear assemblies are the same elements; whereineach of the gear assemblies contains 60 numerals; wherein first andsecond gear assemblies contain the numerals 0 to 60 and wherein a thirdgear assembly contains five sets of the numerals l to 12.

14. A digital clock mechanism comprising:

a plurality of gear assemblies;

a plurality of pinion gears coupling the motion of each gear assembly tothe next gear assembly;

a plurality of numeral carriers rotating simultaneously with the gearassemblies;

a screen;

optical means for forming an image of one numeral from each numeralcarrier on the screen; and

perforated masks driven simultaneously with the rotation of the numeralcarriers and positioned to block numeral projection when the associatedgear assembly rotates.

15. A digital clock mechanism in accordance with claim 14 wherein eachrotating mask is driven by the pinion gear which also drives theassociated gear assembly and numeral carrier.

16. A digital clock mechanism comprising:

a gear train including a plurality of gear assemblies, each one servinga difierent digital time division and including a plurality of gearpinions, each one meshing with and between the preceding and succeedinggear assemblies, and propagating gear rotation from one end of geartrain to the other end, and producing a quick, intermittent and partialturning of each gear assembly in accordance to the requirements of itsdesignated digital time division; plurality of numeral carriers, eachserving a different digital time division and each one numbered inaccordance with the requirements of its designated time division;wherein each said numeral carrier is directly attached to its relatedgear assembly and is simultaneously turned with the said gear assemblythus changing the numerals in the digital display; and an optical systemthat transforms the numerals on said numeral carriers into light imagesrepresenting one digital number at one time for each digital timedivision upon a viewing screen.

1. A digital clock mechanism comprising: a gear support; a gear train formed by having a plurality of gears mounted parallely upon said support, with the edge of each gear engaging the edges of the adjacent gears and with the gears extending longitudinally from one end of the gear train to the other end; a synchronous motor mounted at one end of the gear train; a driver-pacer gear at one end of the gear train that is driven by the synchronous motor, said driver-pacer gear having at least one group of at least one gear tooth spaced about its periphery and adjacent to at least one notch in its periphery; pinion gears and gear aSsemblies comprising the plurality of gears, the first pinion gear transferring the motion of the driver-pacer gear to the first gear assembly, and each succeeding pinion gear transferring motion from one gear assembly to the next; said gear assemblies each including a fully-toothed periphery for engaging the previous pinion gear and a periphery containing at least one tooth and at least one notch for engaging the next succeeding pinion gear; and said pinion gears containing a fully toothed periphery for engaging said tooth on the preceding gear or gear assembly and the fully toothed periphery of the following gear assembly, and a partially toothed periphery for engaging said notch in the preceding gear assembly or driver-pacer gear and for otherwise immobilizing the pinion gear; numeral carriers each of which is rotated by a gear assembly; and means for viewing one numeral on each numeral carrier.
 2. A digital clock mechanism in accordance with claim 1 wherein at least one of the gear assemblies includes a first half of the gear assembly that bears the fully-toothed periphery and a second half of the gear assembly that bears said tooth and said notch, wherein the two halves are coupled together by a ratchet mechanism comprising pins or lugs on one half which engage notches on the other half and spring means for driving the two halves together, and which further includes a manually actuatable time setting mechanism that attaches to one half of the gear assembly but that does not attach to the other half.
 3. A digital clock mechanism in accordance with claim 1 wherein the driver-pacer includes four groups of two teeth centered about four notches which are equally spaced around the periphery of said driver-pacer gear, wherein the pinion gears each have eight teeth about their fully toothed periphery and four teeth about their partially toothed periphery, wherein the diameter of the driver-pacer gear is chosen in relation to the driver-pacer gear tooth size so that approximately 40 teeth of the same size could properly be spaced about the periphery of the driver-pacer gear, and wherein the driver-pacer gear is driven at a speed of 15 revolutions per second by a synchronous motor.
 4. A digital clock mechanism in accordance with claim 1 to which has been added an alarm mechanism comprising: a manually positionable disc bearing the numbers ''''1'''' through ''''12''''; a gear driven through one complete revolution every 12 by means coupling to a gear assembly that rotates at least once every hour; and means responsive to the disc and the gear reaching corresponding positions for sounding an alarm.
 5. A digital clock mechanism in accordance with claim 1 wherein some of the gear assemblies are identically shaped and wherein some of the pinion gears are also identically shaped.
 6. A digital clock mechanism in accordance with claim 1 wherein the means for viewing one numeral on each numeral carrier comprise an optical system including a source of light positioned on one side of each numeral carrier, a screen positioned on the other side of each numeral carrier, and stationary masking means for preventing images of more than one numeral on each numeral carrier from being projected onto the screen.
 7. A digital clock mechanism in accordance with claim 6 wherein the optical system includes a condensing lens positioned between the source of light and each numeral carrier and a projection lens positioned between each numeral carrier and the screen.
 8. A digital clock mechanism in accordance with claim 6 wherein a rotating masking means including at least one opening is provided for each numeral array and is positioned to block the passage of light through the numeral array except when a opening is in line with the source of light, the masking means, and the screen; and wherein each pinion gear is arranged to rotate the rotating masking means associated with the next higher gear assembly in the gear train.
 9. A digital clock mechanism in accordance with claim 6 wherein the numeral carriers are in close proximity to the screen, whereby images of the numerals are formed by the light rays from the light source passing through the numerals and striking the screen without the aid of lens system.
 10. A digital clock mechanism in accordance with claim 9 wherein two arrays of numerals are used to represent the time in seconds, wherein two arrays of numerals are used to represent the time in minutes, and wherein a single array of numerals is used to represent the time in hours; wherein the arrays of numerals representing the units digit of time in seconds and in minutes each contain 10 numerals from 0 to 9, wherein the arrays of numerals representing the tens digit of the time in seconds and in minutes each contain six numerals from 0 to 5, and wherein the array of numerals representing the time in hours contains the 12 numerals from 1 to
 12. 11. A digital clock mechanism in accordance with claim 1 wherein at least one of the pinion gears includes a first half of the pinion gear that bears the fully-toothed periphery and a second half of the pinion gear that bears the partially toothed periphery, wherein the two halves are coupled together by a ratchet mechanism comprising pins or lugs on one half which engage notches on the other half and spring means for driving the two halves together, and which further includes a manually actuatable time setting mechanism that attaches to one half of the pinion gear but that does not attach to the other half.
 12. A digital clock mechanism in accordance with claim 1 to which has been added an alarm mechanism comprising: a manually positionable disc bearing the numbers ''''1'''' through ''''24''''; a gear driven through one complete revolution every 24 hours by means coupling to a gear assembly that rotates at least once every hour; and means responsive to the disc and the gear reaching corresponding positions for sounding an alarm.
 13. A digital clock mechanism in accordance with claim 1 wherein the numeral carriers and the gear assemblies are the same elements; wherein each of the gear assemblies contains 60 numerals; wherein first and second gear assemblies contain the numerals 0 to 60 and wherein a third gear assembly contains five sets of the numerals 1 to
 12. 14. A digital clock mechanism comprising: a plurality of gear assemblies; a plurality of pinion gears coupling the motion of each gear assembly to the next gear assembly; a plurality of numeral carriers rotating simultaneously with the gear assemblies; a screen; optical means for forming an image of one numeral from each numeral carrier on the screen; and perforated masks driven simultaneously with the rotation of the numeral carriers and positioned to block numeral projection when the associated gear assembly rotates.
 15. A digital clock mechanism in accordance with claim 14 wherein each rotating mask is driven by the pinion gear which also drives the associated gear assembly and numeral carrier.
 16. A digital clock mechanism comprising: a gear train including a plurality of gear assemblies, each one serving a different digital time division and including a plurality of gear pinions, each one meshing with and between the preceding and succeeding gear assemblies, and propagating gear rotation from one end of gear train to the other end, and producing a quick, intermittent and partial turning of each gear assembly in accordance to the requirements of its designated digital time division; a plurality of numeral carriers, each serving a different digital time division and each one numbered in accordance with the requirements of its designated time division; wherein each said numeral carrier is directly attached to its related gear assembly and is simultaneously turned with the said gear assembly thus changing the numerals in the Digital display; and an optical system that transforms the numerals on said numeral carriers into light images representing one digital number at one time for each digital time division upon a viewing screen. 